The invention relates to an optical module which contains an optical component with at least one optical input and/or output, wherein an optical input and/or output is directed towards an optical fiber and this input and/or output comprises an optical waveguide whose end, facing towards the optical fibber, is of tapered or widened formation for a modal field adaptation.
The invention is based on a priority application (00440227.7) which is hereby incorporated by reference.
Optical modules for processing light signals contain different optical components, such as purely optical or opto-electric components, for example opto-electric converters (generally laser diodes or photodiodes), amplifiers or modulators. Such components are coupled with optical fibres, normally glass fibres, but optionally also plastic fibres. Among other things, the power output of such optical modules is dependent upon the quality of this coupling.
As the diameter of the modal field at the input and/or output (in the following abbreviated to input/output) of such components is distinctly smaller than that of the modal field in the core of the optical fibre, different techniques have been developed to optimise the coupling. It has long been prior art to provide the input/output of the optical component with a waveguide whose end facing towards the optical fibre is tapered, for example in the form of a frustum, or is widened. Optionally, the waveguide and the core of the optical fibre can lie on the same axis. As a result of the oblique surfaces at the taper (for example the frustum) the modal field is enlarged by the light radiating therefrom, so that ideally a diameter is achieved which is equal to that of the modal field at the input of the optical fibre. Accordingly, modal field converters (xe2x80x9cspot-size converterxe2x80x9d or xe2x80x9ctaperxe2x80x9d) are referred to. Such tapered/widened ends are generally structured directly in the same layer (for example in a semiconductor layer made of doped InP) in which the optical component was formed, either vertically or horizontally or even in both directions of the plane (see e.g. H. Oohashi et al. ECOC97, No. 448, p. 351-354, 1997).
It is also prior art (see e.g. DE 34 15 576) to use miniaturised lenses as modal field converters. This enables the efficiency of this coupling to be considerably increased. However the use of miniaturised lenses has the disadvantage of the extremely poor adjustment. The outlay required to achieve a satisfactory coupling with the high tolerance requirements is correspondingly high.
A combination of taper-like modal field converter and miniaturised lenses partially facilitates a good coupling. However the adjustment problems associated with the miniaturised lenses remain. Consequently the costs of optical modules designed in this way cannot be sufficiently reduced. This remains a considerable obstacle to their further development.
The object of the invention is to further develop an optical module wherein the coupling between optical components arranged thereon and optical fibres aligned therewith is extremely efficient without excessively increasing the costs of such optical modules.
The object is achieved in accordance with the invention by an optical module which contains an optical component with at least one optical input and/or output, wherein an optical input and/or output is directed towards an optical fibre and this input and/or output comprises an optical waveguide whose end, facing towards the optical fibre, is of tapered or widened formation for a modal field adaptation, wherein between the optical waveguide of the optical component and the optical fibre there is arranged an additional optical waveguide whose end, facing towards the optical fibre, is of tapered or widened formation for a modal field adaptation.
The interposition of an additional modal field converter between the input/output of the optical component and the optical fibre to be coupled therewith facilitates a high degree of efficiency for such a coupling without the occurrence of disadvantageous alignment faults, particularly at the edge of the modal field, as is the case when a miniaturised lens is used. Moreover, this additional modal field converter is generally positioned on the optical module using current techniques. For this purpose this additional modal field converter can be separately produced and then soldered or glued onto the optical module.
However, it can also be particularly advantageous to integrate this modal field converter directly in the optical module. For this purpose, the modal field converter is then structured on such optical modules, similarly for example as in the case of optical waveguides. Such optical modules are generally constructed on a silicon wafer (Si-wafer) serving as carrier. The optical waveguides are then integrated in known manner onto such silicon wafers, i.a. by a layer construction of differently doped silicate glasses (SiO2, SiON, . . . ). This considerably simplifies the alignment of the different components onto such an optical module as well as their packaging, i.a. in comparison to the use of miniaturised lenses.
Advantageous developments of the invention are described in the dependent claims, the following description and the drawings.